1. Field of the Invention
The present invention relates to an aromatic polyamide pulp and a process for the preparation thereof. More particularly, the invention is concerned with an aromatic polyamide pulp prepared by a process wherein Lewis acid type compounds and, optionally, inorganic salts are added and dissolved into amide type solvents, urea type solvents or a mixture thereof, followed by pouring an aromatic diamine and an aromatic diacid chloride into the resulting solvent to obtain a highly polymerized aromatic polyamide pulp and a process therefor.
2. Discussion of the Related Art
Various processes for the preparation of aromatic polyamide pulps have been disclosed in the prior art. For example, U.S. Pat. No. 4,511,623 describes a process for the preparation of aromatic polyamide pulp which uses a mixture of an amide solvent, inorganic salts and a tertiary amine as a solvent system. However, there are several disadvantages which result from the use of an excess amount of a tertiary amine. When such an excess is used, the polymerization and gelation proceed so rapidly, i.e. in a few seconds, that the process cannot be controlled. Therefore, the reproducibility is poor. Particularly during gelation, the molecular chains are isotropic and lack orientation; thus, the polymer solution must be maintained for more than 5 hours to obtain a fine fibrous pulp with a high molecular weight. This prior art process using a tertiary amine is very expensive because of the high cost of the tertiary amine compounds. Moreover, the solubility of the polymer is so low that the ratio of polymer to polymerization solvent cannot be increased beyond a certain extent.
Japanese Patent Publication No. 59-47694 describes a process for the preparation of a pulp-like particle by reacting monomers in an amide type solvent for polymerization, immersing the resulting mixture in alcohol and pulverizing. However, in this prior art process, a polymer solution with a low inherent viscosity must be pulverized in water or alcohol so that the ultimate product has a low inherent viscosity of 2.0-3.5. Such a low inherent viscosity results in a deterioration of the properties of the polymer.
U.S. Pat. No. 4,876,040 describes a process in which a liquid crystalline polymer solution polymerized in an amide type polymerization solvent containing an inorganic salt is pressed and sprayed together with a tertiary amine in a pulping machine. However, this process requires an excess amount of an expensive tertiary amine, which results in an expensive product. Moreover, excessive use of tertiary amines produces environmental problems.